The invention relates to machines used for stringing of tennis rackets and the like and particularly to those machines which incorporate structure designed to assist in the obtaining of the desired objective of a uniform tensioning of the strings. U.S. Pat. No. 3,441,275 discloses a machine in which the string is tensioned by manual rotation of a crank causing displacement of a carriage and string clamp away from a fixture holding the racket head and in which the carriage is automatically locked against displacement relative to the head when the string reaches a predetermined tension. U.S. Pat. No. 2,154,870 incorporates a friction clutch in the string tensioning structure so that only a predetermined degree of tension can be imparted to the string. Due, however, to the many factors involved such as varying friction between the engaged strings and racket head, subsequent stress relieving of the strings, and other factors, a variable, uncertain and random loss of string tension will result. Nor is the loss consistent, but will vary from string-to-string and between the longitudinal main strings and the cross strings. The amount of stress release cannot be precisely determined and will vary with size, quality and length of string used and the variable, random friction between contacting strings. Moreover, stress release will occur over a period of time so that the playing characteristics of a racket will change (deteriorate) with use. Accordingly, expert players have come to accept a required break-in period for a newly strung racket. However, even accepting a break-in period, the player cannot know in advance what the ultimate tension and playing characteristics of the racket will be. The above-noted inconsistency may vary anywhere from about ten to twenty pounds from string-to-string, even after the break-in period.